My iPhone 6 Plus

silvea wrote:

I want upgrade my iOS for my iPhone 6 Plus How I can do this?

Yes you can keep your iPhone 6 Plus but you cannot update past iOS 12.5.1.

There's no more update for that iPhone model.

If you really want/need the update then you cannot keep your old iPhone, you have to get a newer iPhone model.

You can't. It doesn't have enough RAM.